It is in DBD::CSV's documentation that it does not handle types correctly. Your specific bug is mentioned.

I believe it was a DBI design decision to not require stringent type handling of database drivers because that would have made it more difficult to create them and because lots of the backends are not strictly compliant. A CSV file doesn't not have an SQL compliant typing system. You may want to type all your fields; the next player may just want it to work.

Be well,
rir